The invention pertains to reinforcing braces for stringed musical instruments, and more particularly, the shaping and positioning of said braces in relation to the nodes of the vibrating plates of such instruments.
Many stringed musical instruments, such as mandolins, violins and guitars are constructed in the form of a hollow box which forms the body of the instrument. This box, which typically consists of a top plate, a back plate and one or more side plates, serves, together with other elements, to support the strings so that they can vibrate properly, and to amplify the sound from the vibrating strings. It is known that the quality of sound radiated by such an instrument depends, in large part, on the structure of the body of the instrument, the nature of the material used for the body, and even the finish applied to the body.
Musical instrument design has been the work of artisans and craftsmen for years, and the production of a quality musical instrument producing a pleasing sound remains a function of both physical design and the experience and skill of the craftsmen. Nevertheless, in recent years, a greater understanding of the various properties of design and materials has been achieved. Numerous experimental scientific studies have been performed in an effort to determine the nature of the variables which, when combined, produce a stringed instrument having the most pleasing sound. An example of this type of study can be found in the article xe2x80x9cThe Acoustics of Violin Platesxe2x80x9d, Scientific American, October, 1981. There, the author summarizes techniques for testing the vibrational properties of the plates of stringed musical instruments. One of the techniques therein described involves the sprinkling of the plate with a fine powder, and thereafter causing the plate to vibrate. At certain frequencies known as eigen frequencies, this vibration bounces the powder into patterns which define the nodal and anti-nodal configurations of the plate at specific resonants frequencies. This work, first pursued in the late 1960""s by Carl A. Stetson has served to define a number of xe2x80x9cmodesxe2x80x9d or vibrational patterns corresponding to particular frequencies. According to Hutchins, the author of the above-referenced Scientific American article, the modes most important in tuning violin plates are modes 1, 2 and 5. Mode 2, for example, defines a generally xe2x80x9cXxe2x80x9d shaped pattern on the plate, whereas mode 5 defines a pair of somewhat semi-elliptical patterns disposed at opposite ends of the plate, each having a distinctive xe2x80x9cCxe2x80x9d shaped configuration.
The various designs of box body stringed instruments which have evolved are also known to present improved acoustical qualities based on the overall thickness of the top, back and side plates. Thicker plates, as a general rule, have less desirable acoustical properties, since greater string energy is required to make a heavier plate vibrate. Thinner plates, on the other hand, while being more acoustically desirable, provide insufficient structural support for the bridge, neck and tail piece. A balance must be achieved, therefore, between the structural integrity of the instrument and its sound qualities. The need for structural reinforcement of stringed instruments is well known, and the number of techniques have been disclosed for providing bracing to certain types of these instruments, for example, as disclosed by Lam in U.S. Pat. No. 6,166,308 and Teel in U.S. Pat. No. 5,952,592. The bracing disclosed in the afore described references, however, essentially disregards the acoustical effects of the application of such bracing. Limited appreciation of the acoustical effects of the application of bracing is disclosed by Itokawa in U.S. Pat. No. 5,396,822, which teaches the application of stiffeners along nodal lines adjacent to the base bar and sound post of a stringed instrument.
My research has taught that this simplified approach to bracing is inadequate, and that utilization of nodal analysis, like that performed by Stetson, provides a remarkably better basis for determining the shape and location of plate stiffeners in stringed instruments. Further, my work has provided valuable insights into the configuration, construction and location of stiffeners placed according to nodal analysis which optimize the acoustical qualities of stringed instruments.
My invention is an improved stringed musical instrument and a method for construction thereof. A stringed instrument of improved acoustical properties can be constructed by first analyzing the nodal and anti-nodal areas of the plates of the instrument utilizing induced vibration. The nodal and anti-nodal areas can be identified using a variety of means. One simple approach is to sprinkle the vibrating plate with granular particles. The vibrations of the plate results in migration of the particles toward non-vibrating areas and away from vibrating areas, facilitating identification of the nodal and anti-nodal areas. Another technique is the utilization of laser interferometry. Variation of the induced frequency results in the optical location of nodal and anti-nodal areas comprising separate modes of vibration dependent upon the frequency of vibration. Once these nodal and anti-nodal areas have been identified, structural bracing can be shaped and applied to the plate, in such a manner as to take full advantage of the natural vibration characteristics of the plate while still exhibiting the necessary strength to provide the structural support required by the instrument.
In one embodiment, improved acoustic qualities are obtained by using Stetson mode 5 nodal and anti-nodal areas, and the application to the anti-nodal areas of stiffeners formed of a laminate of wood and carbon fiber composite glued to the plate. Instruments constructed according to this method have demonstrated improved acoustic qualities together with improved structural strength.